Electromagnetic valve-controlled fuel injection pump for internal combustion engines, especially diesel engines

ABSTRACT

A solenoid-valve-controlled fuel-injection pump for internal combustion engines, in particular diesel engines, has a solenoid valve ( 18 ), whose valve needle ( 17 ) separates a high-pressure region ( 14, 15 ) from a low-pressure region ( 21 ), i.e. connects the high-pressure region and low-pressure region, in the pump housing, via a valve seat ( 16 ); the injection period being controlled by the opening of the solenoid valve ( 18 ). In addition, a low-pressure compensating piston ( 24 ) situated in the low-pressure region ( 21 ) is provided in order to compensate for pressure fluctuations in the low-pressure region ( 21 ).  
     The exceptional feature is that the low-pressure compensating piston ( 24 ), which is positioned coaxially to the solenoid-valve needle ( 17 ), takes the form of a component part that is separate from the solenoid-valve needle ( 17 ). This ensures that the solenoid valve ( 18 ) is opened unhindered and as rapidly as possible by the opening force exerted on the solenoid-valve needle ( 17 ) by the electromagnet.

BACKGROUND INFORMATION

[0001] The present invention relates to a solenoid-valve-controlled fuel injection pump according to the definition of the species in claim 1.

[0002] This principally relates to a so-called distributor-type fuel-injection pump. In the case of such solenoid-valve-controlled injection pumps that are preferably used in diesel engines, the injection period is controlled by the opening of the solenoid valve. In order that the diesel engine achieves good emission figures, the pressure in the line must decrease as rapidly as possible. This can only be achieved by a quick-opening solenoid valve. Solenoid-valve-controlled pre-injection is only possible, using a quick-opening solenoid valve. Therefore, the solenoid valve must be constructed in such manner, that its opening time can be reduced by hydraulic forces.

[0003] Particularly relevant to the present invention are those distributor-type fuel-injection pumps, in which a so-called I-solenoid valve is used. This type of valve construction distinguishes itself in that, in response to deactivation, the flow is radially directed from the outside to the inside. An opening (positive) force is achieved by diverting the flow in the low-pressure range. The force shortens the valve opening times.

[0004] A basic characteristic of the type of valve in question is a low-pressure surface, which is very large in comparison with the pressure-stage surface in the high-pressure region of the solenoid valve. Therefore, relatively large forces already occur in response to small pressure fluctuations in the low-pressure region. These forces cause fluctuations in the opening time, which result in deviations in the injection amount (from stroke to stroke). In order to at least partially compensate for the mentioned forces and thus largely prevent their disadvantageous effects, the valve type in question is provided with a low-pressure compensating piston, which interacts with the solenoid valve. Therefore, the low-pressure compensating piston has the function of producing stable opening characteristics of the solenoid valve.

[0005] DE 4339948 A1, whose subject matter is a fuel-injection pump of the species, belongs to the above-described related art. In the known fuel-injection pump, the low-pressure compensating piston is constructed in one piece with the solenoid-valve needle and positioned coaxially to it, it being practically a continuation of the solenoid-valve needle beyond the valve seat.

[0006] The disadvantage is that, upon terminating fuel delivery, flow is diverted on the low-pressure compensating piston. This diversion of the flow causes a pressure increase that creates a closing needle force. The disadvantageous effect is a delay in the opening of the solenoid valve during fuel-delivery termination.

[0007] The object of the present invention is to take appropriate measures to prevent unwanted delays in opening the solenoid valve.

SUMMARY OF THE INVENTION

[0008] In the case of a fuel-injection pump of the type mentioned at the outset, the object of the present invention is achieved by the characterizing features of claim 1.

[0009] Advantageous further refinements of the root idea of the present invention are derived from claims 2 through 8.

[0010] The features according to the present invention succeed in retaining the advantages of the existing low-pressure compensating piston, which are important for the functioning of the solenoid valve in its closed state. However, the previous, negative effects of the low-pressure compensating piston during the opening of the solenoid valve are simultaneously eliminated.

BRIEF DESCRIPTION OF THE DRAWING

[0011] The present invention is illustrated in the drawing, using an exemplary embodiment that is described in detail below. The drawing shows a vertical, longitudinal cross-sectional view of part of a specific embodiment of a distributor-type fuel-injection pump.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0012] Reference numeral 10 designates a distributor, which is supported in a pump housing (not shown) in a manner that is well known and therefore not shown in detail. The actuation of distributor 10 is accomplished in a customary manner, which is why a detailed description of this may also be omitted.

[0013] A pump working chamber (not shown) is connected, via a pressure duct 11 in distributor 10, to a distributor groove 12, which is on the circumference of distributor 10, and from which the injection lines (not shown) running in the pump housing start out. The injection lines lead, in turn, to an injection valve (which is also not shown).

[0014] In addition, a connecting duct 14, which starts at the distributor groove 12 in the interior of distributor 10, empties into an annular groove 15. Annular groove 15 forms a valve seat 16 for a valve needle 17 of a solenoid valve (only partially shown), which is designated, as a whole, by reference numeral 18. An electromagnet, which actuates solenoid valve 18, is known related art, and therefore does not need to be represented in detail, is situated above solenoid-valve needle 17, at position 19.

[0015] Extending below valve seat 16 is a blind-end bore, which is specified as a whole by reference numeral 20 and has an expansion 21 from which a (further) connecting duct 22 starts out. Connecting duct 22 leads to a low-pressure part of the fuel-injection pump (not shown). Therefore, valve seat 16 and solenoid-valve needle 17 define a high-pressure region 14, 15 and a low-pressure region 21, inside distributor 10.

[0016] Positioned inside blind-end bore 20, coaxially to solenoid-valve needle 17 so as to be axially movable, is a low-pressure compensating piston, of which the half on the left side of a longitudinal center line 23 common to solenoid-valve needle 17 and the low-pressure compensating piston is designated altogether by reference numeral 24, and the half on the right side of longitudinal center line 23 is denoted altogether by reference numeral 25.

[0017] The construction type 25 of the low-pressure compensating piston drawn on the right side of longitudinal center line 23 designates the present related art, low-pressure compensating piston 25 being formed in one piece with solenoid-valve needle 17 at position 26.

[0018] In contrast, the low-pressure compensating piston 24, (of) which (half) is represented on the left side of longitudinal center line 23, is of the construction type according to the present invention. In this case, the exceptional feature is that solenoid-valve needle 17 and low-pressure compensating piston 24 take the form of two component parts, which are separate and, therefore, may be (axially) moved independently of each other. In order to guide low-pressure compensating piston 24, it has a piston rod 27 of reduced diameter, which engages with a cylindrical guide hole 28 introduced into solenoid-valve needle 17. The guidance 27/28 effectively prevents low-pressure compensating piston 24 from tilting (which would otherwise be possible). Cylindrical guide hole 28 takes the form of a blind-end bore, its (upper) end 29 acting as a limit stop that interacts with free end 30 of piston rod 27 of low-pressure compensating piston 24.

[0019] A compression spring (low-pressure compensating spring) 32, whose rear end is supported at the base 33 of blind-end bore 20, abuts against a rear end face 31 of low-pressure compensating piston 24. Low-pressure compensating spring 32 presses low-pressure compensating piston 24 against (upper) limit stop 29 of cylindrical guide hole 28.

[0020] A further exceptional feature is that a rod-shaped counter-stop 34, which is surrounded by low-pressure compensating spring 32, and whose end 35 interacts with the base 33 of blind-end bore 20 that simultaneously acts as the (lower) stroke-limit stop for low-pressure compensating piston 24, is situated at (lower) end face 31 of low-pressure compensating piston 24. At the same time, rod-shaped counter-stop 34 is also used to protect low-pressure compensating spring 32.

[0021] The described set-up and construction of low-pressure compensating piston 24 takes effect during the operation of the fuel-injection pump as follows.

[0022] Upon opening solenoid valve 18, the pressure in high-pressure region 14, 15 is reduced via valve seat 16. This results in a local increase in pressure on solenoid-valve needle 17 and low-pressure compensating piston 24. Low-pressure compensating piston 24 now separates from solenoid-valve needle 17. a The force of the low-pressure compensating piston, which is aligned in the closing direction, is supported at distributor housing 10, via stroke-limit stop 33, 34, 35. The force of the solenoid valve results in solenoid valve 18 opening quickly.

[0023] The hydraulic forces exerted on low-pressure compensating piston 24, which, in the case of the previous one-piece construction of the solenoid-valve needle and low-pressure compensating piston, disadvantageously act in the closing direction of the solenoid-valve needle, are eliminated by the present invention's separate construction of solenoid-valve needle 17 on one side and low-pressure compensating piston 24 on the other side. Therefore, the opening force exerted by electromagnet 19 on solenoid-valve needle 17 has the desirable effect of opening solenoid valve 18 unhindered and thus as rapidly as possible. 

What is claimed is:
 1. A solenoid-valve-controlled fuel-injection pump for internal combustion engines, in particular diesel engines, comprising a solenoid valve (18), whose valve needle (17) separates a high-pressure region (14, 15) from a low-pressure region (21), i.e. connects the high-pressure region and low-pressure region, in the pump housing, via a valve seat (16), the injection period being controlled by the opening of the solenoid valve (18); and a low-pressure compensating piston (24) situated in the low-pressure region (21), in order to compensate for pressure fluctuations in the low-pressure region (21); wherein the low-pressure compensating piston (24), which is positioned coaxially to the solenoid-valve needle (17), takes the form of a component part that is separate from the solenoid-valve needle (17).
 2. The solenoid-valve-controlled fuel-injection pump as recited in claim 1; in a low-pressure compensating piston chamber (20) coaxially contiguous to the low-pressure region (21) in the pump housing, the low-pressure compensating piston (24) being positioned so as to be axially movable in opposition to the resistance of a low-pressure compensating spring (32) acting on the back side of the low-pressure compensating piston (24); wherein, in order to protect the low-pressure compensating spring (32), a stroke-limit stop (32) for the low-pressure compensating piston (24) is provided on the rear end of the low-pressure compensating piston chamber (20) opposite to the solenoid-valve needle (17).
 3. The solenoid-valve-controlled fuel-injection pump as recited in claim 2, wherein a counter-stop (34, 35), which interacts with the stroke-limit stop (33) and has a diameter narrower than the diameter of the low-pressure compensating piston (24), is situated at the (rear) end face (31) of the low-pressure compensating piston (24) opposite to the solenoid-valve needle (17).
 4. The solenoid-valve-controlled fuel-injection pump as recited in claim 1, 2, or 3, wherein the end of the low-pressure compensating piston (24) facing the solenoid valve (18) has a piston rod (27), which extends into a cylindrical guide hole (28) that is introduced into the solenoid-valve needle (17) in the region of the solenoid-valve seat (16), and is used to guide the low-pressure compensating piston (24).
 5. The solenoid-valve-controlled fuel-injection pump as recited in claim 4, wherein the cylindrical guide hole (28) has a limit stop (29) for the piston rod (27) and therefore for the low-pressure compensating piston (24).
 6. The solenoid-valve-controlled fuel-injection pump as recited in claim 2, wherein the low-pressure compensating piston (24) is guided in the low-pressure compensating piston chamber (20) independently of the solenoid-valve needle (17).
 7. The solenoid-valve-controlled fuel-injection pump as recited in claim 6, wherein the low-pressure compensating piston (24) is axially supported in the pump housing (10) by the stroke-limit stop (33) and the counter-stop (34).
 8. The solenoid-valve-controlled fuel-injection pump as recited in one or more of claims 5 through 7, wherein the low-pressure compensating spring (32) is designed in such a manner that, when the solenoid valve (18) is closed, the force of the low-pressure compensating spring (32) causes the piston rod (27) of the low-pressure compensating piston (24) to abut against the limit stop (29) in the cylindrical guide hole (28). 